From the German patent DE 103 12 588 A1, a method is already known, in which a vacuum is produced in a fuel tank by way of a pump. The pressure is measured in the gas volume of the tank. If the increase in pressure occurs faster than that which is known for an impervious fuel tank system, a leak is detected.
Additional methods for testing for leaks, especially in a fuel tank ventilation system of a motor vehicle, are, for example, known from the German patents DE 41 24 465, DE 19636 431, DE 198 04 384 and also DE 196 25 702. In these methods, the fuel tank ventilation system is pressurized with an excess pressure; and by a subsequent evaluation of the pressure profile, the presence of a tank leak can possibly be suggested.
Methods are additionally known from the Japanese patent JP-6-173837 and the American patent U.S. Pat. No. 5,247,971, in which a reference leakage is switched in and in which a conclusion is drawn about the presence of a leak by comparing the measurements with or without the reference leakage.
Common to the methods is that a definite state of origin, respectively starting pressure, is initially set for the detection of leaks. After this the pressure profile which ensues is measured, whereby at least the one pressure sensor is disposed in the gas volume of the fuel tank or in that of the fuel tank ventilation system. If the measured pressure profile deviates significantly from an expected pressure profile, it is typically assumed that a leak is present in the fuel tank, respectively in the fuel tank system.
Additional pressure sensors, which, however, are not for the detection of tank leaks but for the acquisition of the fill level, are known, for example, from the American patent U.S. Pat. No. 6,282,953. Provision is made here for two pressure sensors, which project into the fuel, to be disposed vertically to the alignment of the bottom of the fuel tank. Said sensors acquire a pressure of the fuel. Additionally a pressure sensor is disposed on the top of the fuel tank, which acquires the pressure of the gas volume above the liquid fuel. A fill level of the fuel tank capacity is ascertained when the pressures measured at all three of the sensors are taken into account.